Due to perceived shortcomings in some aspects of hazard assessment for chemicals administered to aquatic systems, experiments were conducted to determine the effects of copper on various ecological parameters in artificial streams and microcosms. Effects investigated were colonization and growth of periphyton communities in artificial streams, community composition and nutritional content of periphyton in these streams, leaf conditioning and nutritional content in laboratory microcosms, and nutritional suitability of these leaves to a shredding macroinvertebrate. Main effects observed in periphyton growth experiments were significant reduction in substrate colonization due to copper treatment, which led to significantly lower standing biomass in treated streams. Observed growth rates were generally similar between control streams and copper treated streams. Light treatments did not affect periphyton responses to copper. Community composition of the periphyton was affected by 2.5 μg/L copper. Periphyton phosphorus and nitrogen contents were not affected by copper treatment. Conditioning rate of leaves was significantly decreased by 50 μg/L copper treatments in some cases. Leaf phosphate and nitrogen contents were not significantly affected by copper treatment. Significant differences in nutritional suitability of copper-treated leaves to a shredding macroinvertebrate were not detected. These experiments suggest that aquatic primary producers are more sensitive to copper than heterotrophs. Additionally, adverse effects on periphyton were observed at concentrations well below measures of chronic toxicity to organisms dependent on periphyton as a trophic resource and the chronic criteria for copper. As such, greater emphasis should be placed on the sensitivities of periphyton communities in future copper criteria determination. / Ph. D.